Webb discovers methane and carbon dioxide in an exoplanet over 8 times bigger than Earth

Astronomers using the James Webb Space Telescope have discovered methane and carbon dioxide in the atmosphere of K2-18 b, an exoplanet 8.6 bigger than Earth. 

The abundance of carbon-bearing molecules and shortage of ammonia in this intriguing world supports the hypothesis that there may be a water ocean underneath a hydrogen-rich atmosphere of the exoplanet that orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth.

Recent studies suggest that K2-18 b could be a Hycean world - one which has the potential to possess a hydrogen-rich atmosphere and a water ocean-covered surface. Some astronomers believe that these worlds are promising environments to search for evidence of life on planets beyond our solar system.

"Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere. Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations," explained Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper.

Webb's initial observations also provided a possible detection of dimethyl sulfide (DMS), a molecule which is only produced by life on Earth. However, the inference of this molecule is less robust and requires further validation, the researchers said.

The team analysed light from K2-18 b's parent star as it passed through the exoplanet's atmosphere. K2-18 b is a transiting exoplanet, meaning astronomers can detect a drop in brightness as the planet passes across the face of its host star.

During transits, a tiny fraction of starlight will pass through its atmosphere before reaching telescopes like Webb. The starlight's passage through the exoplanet atmosphere leaves traces that can be pieced together to determine the gases of the exoplanet's atmosphere.

The team now plans to conduct follow-up research with Webb's MIRI (Mid-Infrared Instrument) spectrograph, which is further expected to validate their findings and provide new insights into the exoplanet's environmental conditions.

"Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the universe. Our findings are a promising step towards a deeper understanding of Hycean worlds in this quest," concluded Madhusudhan.